University of Queensland coastal erosion researcher Konrad Beinssen, who is based on North Stradbroke, said the beach erosion at Jumpinpin was a flow slide, not a sinkole and was likely triggered by sand flowing away and starting an initial underwater sand cliff.

"These are things that get triggered offshore in underwater channels, these things can be triggered and they will move upslope and sometimes they peter out and sometimes they move up to the beach," Mr Beinssen said.

"If you get fine tightly packed sand on a submarine slope, which is vulnerable to collapse, all you need is a trigger and just like a bushfire, it will grow and grow and grow."

Mr Beinssen said flow slides are common anywhere there is an underwater channel and often go unnoticed as they rarely make it to the beach.

However when they do, then can be damaging.

"They are very common but you don't often see them because they occur underwater and they peter out before they get to the bank," Mr Beinssen said.

"They don't last for very long. They start underwater and they are unpredictable.

"Sometimes they are quite small and go unnoticed but sometimes they proceed up the beach and into the bush."

It is likely the flow slide will happen again.

"When sand moves again, it will gradually fill, it will get to a new slope, new sand will move in, it will pack itself down densely and then it will happen again," Mr Beinssen said.

University of Queensland coastal engineer Professor Peter Nielsen, who has studied rapid beach erosion at Rainbow Beach and Amity Point on the north-east point of North Stradbroke, confirmed it could not be a sinkhole.

"We don't have cavernous substrates here geologically. That idea of a sinkhole would require having something like a limestone cave that all of a sudden gets filled up with water and sand, and there are no such caves in the geology around here," Professor Nielsen said.

"The one at Rainbow Beach and Amity Point, they are definitely not sinkholes, they are particularly rapid beach erosion events, where it looks as though the sand has a vertical cliff underneath the water.

"That is probably what is giving people the impression that sand is going into a sinkhole."

Professor Nielsen said the action was similar to an underwater avalanche.

"You get the impression that the retreating beach is like a vertical cliff under the water and that is very unusual.

"The near vertical erosion face of the sand requires the sand to be compacted, waves will do that.

"It's a bit like an avalanche."

Professor Nielsen said it would only stop when it reached a stable point.

"The erosion rate is very fast, the shoreline can move back at several metres per minute sometimes," Professor Nielsen said.

"It will go on until it usually stops when it hits a rock wall, it will also stop if it gets to tree roots that stabilise the sand so it can't go any further."